This invention relates to an ignition timing control method for internal combustion engines and, more particularly, to a method of this kind which is capable of adjusting the ignition timing to an optimal value in a simple manner at the time of delivery of the engines from the plant as well as at the time of maintenance operation.
There is known an ignition timing control method for internal combustion engines which includes reading from memory means (e.g. ROM) basic advance angle control data corresponding to basic operating parameters of the engine, e.g. engine rotational speed and intake passage absolute pressure as load on the engine as well as correction advance angle control data corresponding to engine coolant temperature, intake air temperature, etc., calculating ignition timing optimal to engine operating conditions on the basis of the read basic advance angle control data and correction advance angle control data, and controlling conduction of the ignition coil and interruption of same by the ignition timing thus calculated.
However, there can occur variations in operating characteristics or performance between engines in different production lots. As a consequence, if the ignition timing obtained based upon advance angle control data which is determined in the trial manufacture is applied to engines which have different operating characteristics, knocking can occur in a particular operating region. Although knocking which occurs in low load conditions of the engine does not form a grave problem, knocking which occurs in high load conditions of the engine badly affects the operation of the engine.
One way to solve this problem would be to rewrite the whole contents in fixed memory means in which advance angle control data are stored, or replace the fixed memory means with different ones. However, it requires a great deal of labor and time, and accordingly invites a high cost.
On the other hand, the manner of controlling engine operation has become more and more complicated with recent progress of control technology for internal combustion engines, and the quantity of control data is increasing accordingly. Therefore, it is necessary to employ memory means with an increased capacity so as to cope with the increasing quantity of control data to be stored, without incurring an increase in the cost.
However, the whole quantity of data to be stored in memory means, that is, basic control data and correction control data, will be immense. Therefore, if a control unit is so constructed that correction control data are stored in memory means different from those for storing basic control data, it will invite a greater increase in the product cost. It is therefore desirable to reduce the quantity of basic control data and correction control data to be stored in memory means.